The invention is based on a valve control device for controlling the opening and closing times of a motor valve of an internal combustion engine, the motor valve being actuated by a valve control cam of a camshaft via an axially displaceable valve tappet.
In a known valve control device of this type (German Patent Document P 35 32 549.6), an electromagnetic control valve controls the inflow and outflow of pressure medium between the stroke transmission chamber and the return reservoir. The control valve is disposed in the pressure fluid line that connects the stroke transmission chamber with the return reservoir. By opening the magnetic valve, the pressure fluid line is opened up, and the pressure fluid, under the influence of the valve control cam pressing against one side of the stroke transmission chamber and the valve tappet pressing against the other side of the stroke transmission chamber, flows out of the stroke transmission chamber into the return reservoir, which decreases the axial length of the stroke transmission chamber. Despite a further stroke motion of the valve control cam in the direction of valve opening, the valve tappet can thus move toward the valve control cam, under the influence of the valve closing spring, and thereby close the valve. Depending on how the instant of closing is set, the quantity of fuel mixture aspirated into the cylinder can be adapted to the varying requirement for various operating states. As soon as the pressure of the valve control cam lets up, the pressure fluid flows out of the return reservoir back into the stroke transmission chamber, via a bypass line that bypasses the magnetic valve, and the outset situation for the next valve opening phase is thus re-established. It is important in this connection that this should take place with as little delay as possible, even at high engine and hence camshaft rpm, because the valve opening times determine the fuel mixture metering, and this quantity should be adapted accurately to requirements at a given time, to attain the most complete possible combustion, with low toxic emissions. The delay is less, the shorter the route between the reservoir and the stroke transmission chamber. In the aforementioned known valve control device, the return reservoir is located at a relatively great distance from the stroke transmission chamber, adjoining the magnet control valve at the end of the pressure fluid line in the cylinder head. Aside from the relatively long routes that the pressure fluid must take between the stroke transmission chamber and the reservoir, the space required by the return reservoir and the production cost for the engine cylinder head are also disadvantages.